Conductivity probes are used in numerous applications to measure the conductivity of fluids for use in various types of analyses. For example, conductivity probes are commonly used in connection with warewashing operations to monitor the conductivity of a chemical solution being applied to eating and kitchen utensils. In such uses, the conductivity of the chemical solution represents the ionic and/or acidic concentration within the chemical solution relative to pure water, and thus indirectly indicates the percent concentration of one or more component chemical products making up the chemical solution. The use of conductivity probes to facilitate warewashing operations is described in greater detail in U.S. Pat. No. 4,733,798, issued to Brady et al. on Mar. 29, 1988.
Conventional design for conductivity probes involves placing a first magnetic circuit in an arrangement relative to a second magnetic circuit. The magnetic circuits are typically toroidal in shape, and consequently have an inner circumference and an outer circumference. For this reason, these magnetic circuits are commonly referred to as “toroids.” Toroids include a ferrite core between the inner and outer circumferences around which wrapped a conductive wire, which is commonly referred to as a “coil winding.”
In operation, both toroids of a conductivity probe are submerged in a fluid and a current is induced in the wire of the first toroid, thereby generating a perpendicular electric field within the fluid. This electric field induces a current in the fluid that passes through the center of the second toroid. The ferrite core of the second toroid is consequently magnetized thus generating a current in the associated coil winding. The resultant electrical output of the wire winding of the second toroid indicates the conductivity of the fluid. Such a design is very typical of most conductivity probes on the market with the first magnetic circuit being referred to as a “driving toroid” and the second magnetic circuit being referred to as a “sensing toroid.” For example, U.S. Pat. No. 5,157,332, issued to Philip Reese on Oct. 20, 1992, describes one such design for a conductivity cell as well as an improved design having three toroids.
Most conductivity probes include a housing that protects the driving and the sensing toroids from their applicable environment. More particularly, the housing prevents any fluid being measured from entering the toroid wirings, while at the same time, providing a medium through which electric fields may pass without substantial field loss. FIG. 1 depicts an exemplary housing 102 in connection with an illustration of the construction of a conventional conductivity probe 100.
The conductivity probe 100 is constructed using a manual process in which a first toroid 108 and a second toroid 110 are inserted into a toroidal shaped compartment 103 of the housing 102. The toroidal shaped compartment 103 includes an outer circumferential wall 104 and an inner circumferential wall 105, thereby forming a passageway 106 that enables fluid to pass directly through the toroidal shaped compartment 103. The inner circumferential wall 104 and the outer circumferential wall 105 are spaced with respect to one another to accommodate the toroids 108 and 110.
Potting compound, which is not shown in FIG. 1, is commonly used to fill the empty space in the toroidal shaped compartment 103 between and around the toroids 108 and 110. After the toroids 108 and 110 and the potting compound have been placed in the toroidal shaped compartment 103, a toroidal cap 115 is welded on the compartment 103 such that the compartment 103 is enclosed to protect the windings 112 and 114 of the toroids 108 and 110 from being directly exposed to a fluid environment.
As noted above, each toroid 108 and 110 includes a ferrite core 109 and 111 around which is wrapped a conductive wire thus forming windings 112 and 114. The wires each include a pair of connection leads 116 and 118. A first pair of connection leads 116 extends from the first toroid 108 as a part of the conductive winding 112 wrapped therearound. A second pair of connection leads 118 extends from the second toroid 110 as a part of the conductive winding 114 wrapped therearound.
The conductivity probe 100 includes a hollow neck 107 through which the first and second connection lead pairs 116 and 118 are loosely fed while the toroids 108 and 110 are being placed into the toroidal shaped compartment 103. The connection lead pairs 116 and 118 provide an electrical communication interface to a controller (not shown), such as, for example, a warewash controller, at the distal end of the hollow neck 107 relative to the toroidal shaped compartment 103. Using these connection leads 116 and 118, the controller operates the conductivity probe 100 in its intended manner, i.e., to monitor conductivity of a fluid environment. More particularly, a first pair of the connection leads 116 provides an electrical input interface to the controller while a second pair of the connection leads 118 provides an electrical output interface to the controller. That is, current induced in the first pair of connection leads 116 by a controller is communicated to the first toroid 108, which consequently generates a perpendicular electric field in proximity to the toroidal shaped compartment 103. The generated electric field is thus applied to the fluid environment in which the toroidal shaped compartment 103 is submerged while the current is being induced in the first pair of connection leads 116.
The electric field, which affects any ions and other particles having electrical characteristics present in the fluid environment, excites the second toroid 110 thereby generating a current within the coil winding 114 that is communicated by way of the second pair of connection leads 118 to the controller. The electrical output at the termination of the second pair of connection leads 118 indicates the conductivity of the fluid environment, as measured based on the degree that the electric field affects the ions and other particles in the fluid environment.
The above-described method for constructing the conductivity probe 100 shown in FIG. 1 has several drawbacks that seriously undermine the accuracy of measurements taken by the probe 100 over its effective lifetime. While potting compound provides for a decent medium for physically separating the toroids 108 and 110 from one another and the inner circumferential wall 105, it does not provide a tight, rigid contact with respect to the conductive windings 112 and 114. Therefore, over the lifetime of the probe 100, the spacing of the windings 112 and 114 around the ferrite core inevitably becomes inconsistent and the windings tend to loosen. Furthermore, keeping in mind that it is optimal to have the windings 112 and 114 cover the entire 360 degrees around the ferrite cores 109 and 111, the above-described design tends to result in relatively wide separation of the windings 112 and 114 at or around the proximal of the connection lead pairs 116 and 118 relative to the toroidal shaped compartment 103. In addition, loose placement of the connection lead pairs 116 and 118 within the hollow neck 107 often results in electrical interference, or “noise,” between the lead pairs 116 and 118 when carrying current.